This occurs most frequently when someone signs into the program and does not sign out. So, even if you can't see it, the program may still be running on the computer.
First, look at the bottom of your screen ( the task bar ) for the 
icon. If you see it, click on it and see if the program displays on the screen.
If that fails, press the Ctrl-Alt-Del buttons simultaneously, then select Task Manager. Click on the left tab of the window that pops up ( Processes ). If you see Shop Service Writer displayed, highlight it, then click on the End Task button. That will close the hidden, running, program.
You should now be able to enter the program. If you get an error message, call for support.